For perhaps hundreds of years wigs have been commonly used to hide a bald head. Various types of wigs have been proposed, a recent one of which is to be found in U.S. Pat. No. 3,645,276 of Chaihyung Cho. However, a consistent problem with wigs is that they have a tendency to easily slide off the head, particularly under windy conditions or when one engages in athletics.
More recently, methods been proposed for simulating the appearence of having live hairs on the bald head. Thus, one proposal is shown in U.S. Pat. No. 3,642,010 to Kuris, where a supplemental hair consisting of natural hair or synthetic hair is joined to a live hair on the human head by the use of ultrasonic energy. However, it is very difficult to hold supplemental hairs on the human head over a long term. The supplemental hairs easily fall off after only a short term, because the live hairs are usually very thin and weak and have a tendency to break.
In recent years, artificial hair for direct implantation into human skin has been developed. However, the presently available artificial hair for implantation is not completely satisfactory because the shape of the hair root in the artificial hair does not enable the hair to be fixed firmly in place.
One proposal for solving this problem is shown in British patent 2006048A, wherein an artificial hair made of a monofilament resin has a loop part at the end thereof, the hair root being formed by tying the loop part vertically. The disadvantage of this arrangement is that the loop part is easily untied if it is wound singly. If the loop part is wound doubly or more, the knot is enlarged greatly with respect to the diameter of the hair root. When this type of hair is implanted, great injury is caused to the skin, resulting in much of the implanted hair falling out just after implantation. It is generally necessary to pull off the planted hair if inflammation or suppuration occurs on the skin after the hair has been fixed in place. However, with the artificial hair having a loop at the end thereof, if subcutaneous tissue has interpenetrated the loop part, the pulled hair is snapped off at the joint of the knot, leaving the hair root part in the skin tissue which may cause additional medical problems.
To eliminate the above disadvantages, the present inventor previously proposed, in U.S. Pat. No. 4,588,408, of yamada to provide artificial hair which can be pulled out without leaing the root part in the skin tissue. In this instance, intersecting parts of looped hair root were fusion bonded using high frequency spot welding. This gave a freely adjustable peeling strength to the intersecting parts of the hair root. Accordingly, if a planted artificial hair is pulled with a force greater than that of a specified value, the bonding is peeled at the intersection, and the loop shaped hair root becomes a single line of monofilament which can be pulled off without being left n the skin.
However, since the artificial hair is bonded at only one point of intersection at the joint of the loop shaped hair root part, considerably firm fusion bonding is necessary to obtain the critical peeling strength at the intersection, in order to bear the pulling force. If this is the case, the fusion-bonded part becomes too thin, making it more likely that the monofilament will be snapped at the thinned part. Therefore, the conditions for fusion bonding, such as the welding force of a high frequency spot welding device, welding time, frequency of welds, etc., should be controlled carefully. Therefore, the percentage of defective products may increase considerably.